Stan is a probabilistic programming language implementing full Bayesian statistical inference.

Homepage: http://mc-stan.org/

GitHub: https://github.com/stan-dev/stan

AUR: https://aur.archlinux.org/packages/stanc/

I'm not sure how the package should be named. Perhaps stan, but there's an AUR called stan which is a totally different package. Perhaps stanc, as in this AUR. Or then mc-stan as the name of the website. I'd vote for stan.

There are also different interfaces that might be of interest (e.g., Python, R): http://mc-stan.org/interfaces/

If help is needed with this or some other package requests I've made, I'm happy to (try to) help, if asked and told how.